1. Field of the Invention
The present invention relates generally to an annular flow channel for maintaining uniform flow in the channel and for separating cells and particles in a radial force field.
2. Background
In general, particle separation devices take a variety of structures, depending upon the particles to be separated and the separation method to be employed. Particle separation devices separate particle populations into fractions of interest from a suspension and/or other types of particles. The principal method of operation of early particle separation devices relied on a particle's physical parameters to distinguish it from a suspension and/or other types of particles. Examples of these bulk separation techniques include filtration (which is based on particle size), and centrifugation (which is based on particle density and size). These techniques are effective as long as the particle population of interest is significantly different, with respect to size or density, from the suspension and/or the other particles in the population. Additional examples relate to multistage magnetically assisted separation technologies (MAGSEP), as disclosed in Vellinger, et al. U.S. Pat. Nos. 6,312,910 and 6,699,669.
As a subset of bulk separating, continuous separation techniques also exist. The continuous separation of particles in flowing solution requires a well-defined and well-controlled fluid flow pattern. Typically, continuous particle separation devices employ rectangular separation channels. The rectangular geometry of such separation channels provides several advantages including, for example, ease of manufacture, ease of control of fluid flows inside the channels, and ease of design and implementation of forces that drive the separation.
However, rectangular separation channels also suffer from a drawback known as the sidewall effect. The sidewall effect distorts the fluid flow pattern at the side walls of the rectangular separation channel and, hence, adversely affects the performance of the sorting device such as, for example, its resolving power. Therefore, it is desirable to provide methods and devices for separating particles that do not suffer from sidewall effects and can employ any one of a diverse number of separation forces.
Development in the art stemmed from the evolution of various Field-Flow Fractionation (FFF) techniques, as generally discussed in Myers, “Overview of Field-Flow Fractionation,” Journal of Microcolumn Separations, vol. 9, issue 3, pages 151-162, January 1997, John Wiley & Sons, Inc., the entire disclosure of which is incorporated by reference herein. In FFF, a force field is directed perpendicularly across a laminar flow in order to focus particles into narrow bands based on a particular physical characteristic (such as size, molecular weight, charge, etc.) for analysis. Modifying the FFF technique by adding two additional flow streams and an inlet and outlet splitter surface effectively creates a split-flow thin separation channel. This channel allows the operator to fractionate the sample based on a physical characteristic and collect the positively and negatively selected fractions for further analysis or utilization.
Several rectangular embodiments of split-flow thin separation channels exist that attempt such separation using various driving forces including (but not limited to) gravitational, electrokinetic, thermal diffusion, centrifugation, and magnetophoretic. Recent embodiments of said channels utilize an approach where the negative impacts of the sidewall effects are eliminated by wrapping the separation channel around a cylinder and directing the flow paths parallel to the axis of the cylinder. The resulting geometry provides an annular separation volume that is contained between two concentric walls as disclosed in Aitchison et al. U.S. Pat. No. 4,141,809 and in Zborowski et al. U.S. Pat. Nos. 5,968,820 and 6,467,630B1. In one embodiment, a quadrupole magnet is used to generate a magnetic field with concentric B contour lines, thus providing a radial driving force in the annular separation volume that separates magnetic particles towards the outer wall of the annulus as disclosed in Zborowski et al. U.S. Pat. Nos. 5,968,820 and 6,120,735. While these devices have seen some success in the laboratory, the prior art still contains drawbacks that have prevented the introduction of these devices into conventional practice.
In order for the split-flow thin separation process to provide a successful separation, it is essential that the sample and carrier solutions each form circumferentially consistent laminar flow profiles prior to engaging at the inlet splitter tip. Additionally, it is desirable that this flow profile be achieved for a wide range of inlet flow rates for both the sample and carrier solutions. Although prior art devices have produced a degree of circumferential distribution over some flow rate ranges, a need exists for better distribution over a wider range of flow rates. Furthermore, prior art devices suffer from an inability to be easily manufactured and assembled in an inexpensive, repeatable, and precise manner by, for example, injection molding techniques. A need exists for an apparatus that can provide multiple splitter diameters by machining and that can provide a single injection mold with simple interchangeable core pins that can manufacture splitters for a wide range of diameters and optimized flow regimes while being mechanically robust and not prone to breakage.